Carl Mears is lead author for the Climate Science Special Report: Fourth National Climate Assessment, volume I, U.S. Global Change Research Program. He is also a senior scientist with Remote Sensing Systems in Santa Rosa, where he specializes in satellite-measured temperature data. He’s on the board of the Center for Climate Protection and is a member of the Sonoma County Climate Action Advisory Committee.

As was recently reported in The Press Democrat, the U.S. government recently released the first volume of the Fourth National Climate Assessment. As one of the 51 authors of the report, (and the only one from the private sector), I was relieved that there was no political interference in the writing and editing process. The report accurately represents the conclusions of the expert scientists on the writing team.

The report is 477 pages of fairly technical reading, so I doubt that most people are ready to read it cover to cover. But I can summarize it in just three sentences:

Global warming is happening now.

It’s caused by human activities, mostly emission of carbon dioxide.

And the consequences are beginning now — and becoming increasingly serious as the warming continues.

These statements are not the personal opinions of the writing team. Every “key finding” in the report is defended by a “traceable account” that describes the scientific reports we read and synthesized to reach that conclusion.

Since this column is titled “Close to Home,” I thought I’d highlight several new findings that are of special concern to Californians and residents of Sonoma County.

Our report is the first to address sea level rise while considering troubling new results about the stability of ice sheets in Antarctica. By 2100, the expected range of sea level rise is between one and four feet. But because we do not know exactly how the ice in Antarctica will respond to warming oceans, a sea level rise of eight feet cannot be ruled out. This amount of sea level rise would flood a lot of low-lying land around the San Francisco Bay, including significant parts of downtown Petaluma.

Much of California depends on the Sierra snowpack to store water. New, more advanced climate models are able to predict the state of the spring time snow in the Sierra. Unless we begin to curtail carbon dioxide emissions soon, warming temperatures will lead to rising snow levels and more wintertime precipitation will fall as rain in the Sierra Nevada. Under the assumption of continued high carbon dioxide emission, the snow levels increase by more than 1,000 feet, leaving much of the mountain region north of Interstate 80 snow free at the end of the winter. The water that should flow down the rivers in July and August comes much earlier in the year, threatening vital infrastructure such as dams and levees and reducing the amount stored for summer use.

Another consequence of warming temperature is the drying of soil and vegetation during our long, dry summers. Last month’s tragic fires bring the threat of wildfire to the forefront of our attention.

Because of dryer summer conditions, and the large swaths of dead trees killed by the warmer, more stressful climate, our report concluded that wildfires will increase over the entire western United States, a trend that has already been measured in almost every region of the West.

Drier conditions will also increase the need for irrigation, even as our state’s capacity to store water is reduced by the dwindling snowpack.